1. Field of the Invention
This invention relates to a method for cooling components of installations charged with flowable media, in particular molding units for glass melts, and/or for the direct cooling of molded glass parts. This invention further relates to a device for executing the method.
2. Description of Related Art
A basic problem in connection with molding glass is related to the selection and the temperature of the cooling medium for the molding unit. With indirect cooling, which acts on the glass melt through a cooling conduit and the customarily metallic molding unit, a temperature gradient is created leading to a resultant glass contact temperature, which logically lies between the glass temperature and the temperature of the cooling medium.
Cooling media, such as air, compressed air, or air from a blower, water and oils are customary cooling media. Each cooling medium has specific advantages and disadvantages, which helps decide their possible technical use.
For example, air can be blown through a cooling conduit in a turbulent manner, such as by compressed air, or in a turbulent-laminar manner, by blower air. The cooling effect can be varied over a wide temperature range, which is determined by the flow rate, the pressure which determines the flow conditions, and the specific heat capacity (cp 1.00 kJkgxe2x88x921 Kxe2x88x921), which is a specific property of all materials. The heat capacity decides how much energy is absorbed by a material when the temperature is increased. The resultant cooling effect is even less for gaseous materials with low capacity by volume, if the volume which is sent through the respective cooling conduit, on an order of magnitude of 5 to 50 Nm3/h, is made the basis, instead of the weight.
Water is always used in glass technology as cooling medium when the cooling effect of air is insufficient. However, the cooling effect is drastically increased in comparison to air. This is mainly the result of the heat capacity (cp 4.19 kJkgxe2x88x921 Kxe2x88x921), which leads to large amounts of heat being removed at only small temperature changes. A strong cooling effect is particularly disadvantageous if the glass contact temperature is dropped below the transformation range of the respective glass, in this case tears and folds can arise in the glass flow, which lead to the respective products becoming scrap. The employment of water is always difficult, if not impossible, if setting the glass contact temperature over a wide temperature range is in a controlled manner. Also, the dead volume in the cooling conduit leads to evaporation of the water, which can greatly hamper a definite flow rate of the water, is also problematical. The relatively low evaporation temperature of 100xc2x0 C. has also disadvantageous effects. It is possible to increase the evaporation temperature by increasing the pressure, but not in the desired amounts in order to be able to clearly expand the process window.
Oil as a cooling medium has the advantage of having a heat capacity which lies below that of water. But because of their flash points, oils make increased demands on the installation technology, which can only be used in certain processes.
It is one object of this invention to provide a method and a device for executing the method, which operate at a resultant cooling effect between that of air and water, without it being necessary to change the existing installation structure or the installation components for hot-molding flowable materials, for example glass, and which are also usable for the direct cooling of molded glass articles.
In connection with a method of this invention, this object is achieved with a mixture of compressed and/or blower air and a water aerosol fog is used as the cooling medium.
This cooling medium mixture is very stable in continuous operations, and also cost-effective and so universal, that it can cover the controlled temperature range for hot-molding demanded in glass technology, and can also be used for direct cooling of the molded glass articles.
The cooling effect can be changed by the flow rate of the compressed and/or blower air and the proportion of the water aerosol fog. For one, the cooling effect of this cooling medium mixture is based on heating processes, and for another also on evaporation processes.
While in connection with air cooling the cooling effect is customarily regulated by the amount of air, only the flow rate of the amount of air is maintained constant at approximately 10 Nm3/h, and the amount of water is regulated to be between 0 and 8 l/h. However, the cooling effect can be further increased if, with identical amounts of water, the compressed and/or blower air supply is lowered to 6 Nm3/h, and the water portion in the resulting mixed medium is additionally increased.
The cooling effect can be set over a wide temperature range, which achieves the cooling effect of compressed and/or blower air, as well as almost the cooling effect of water, as proven by practical measurements. Water includes a narrow temperature range of approximately 20xc2x0 C. to 70xc2x0 C., while a temperature range from 500xc2x0 C. down to 280xc2x0 C. can be governed by compressed and/or blower air which, however, must not be downwardly exceeded. With the novel cooling medium mixture it is possible to bridge the gap between air cooling and water cooling.
For improving comminution, in one embodiment the amount of water is superimposed on the compressed and/or blower air by using a water nozzle.
Stability of the cooling medium mixture of compressed and/or blower air with a water aerosol fog in continuous operation is achieved by the fine atomization of the water and the rotating movement of the carrier medium of air in the mixing nozzle. This also applies to a defined length into the cooling conduits of the molding unit. The mixing of both media should take place as closely as possible to the molding unit in order to prevent the extremely finely distributed water droplets from agglomerating into larger ones.
This mixing medium for cooling makes greater demands on the medium supply necessary. In accordance with one embodiment, filtered deionized water is used for the aerosol fog.
One important advantage is that the fine regulation of the glass contact temperature which, with some technical applications, remains stable just above the so-called adhesion temperature, for example the temperature at which the formed-out glass wets the mold surface.
In principle, the cooling medium mixture can be used in all cases of cooling. It can be used for a constant feed, as well as for technical requirements which rapidly change from a strong to a weak cooling effect, and vice versa. In this case it is also possible to operate with constant compressed and/or blower air, and the cooling medium can also be directly aimed on the surfaces of the molded glass articles, which are free in the molding unit, or on the molded glass article taken out of the molding unit.
A device for executing the method in accordance with this invention is distinguished, somewhat because compressed and/or blower air is radially introduced into a cylindrical mixing chamber. Water can be supplied to a centered, axially oriented mixing pipe in the mixing chamber, which is closed off by a water nozzle. The compressed and/or blower air rotating around the mixing pipe is mixed with the water aerosol fog exiting from the water nozzle and can be supplied via the adjoining outlet of the mixing chamber directly to the installation component, such as the molding unit, or is directed on the free surfaces of the glass article to be cooled.
The water, which is centrally fed into the mixing chamber, is finely atomized by the water nozzle which closes off the mixing pipe. Such nozzles are commercially available. The compressed and/or blower air is tangentially fed in, in order to obtain a rotating gas movement in the mixing pipe. The water aerosol fog is superimposed on the compressed and/or blower air in the mixing chamber, and a mixture is emitted at the outlet of the mixing chamber and is directly conducted to the cooling conduits of the installation component, such as the molding unit. The connection is provided by pressure lines.